A systematic review assessing the existence of pneumothorax-only variants of FLCN. Implications for lifelong surveillance of renal tumours

Abstract

Individuals with Birt-Hogg-Dubé syndrome (BHDS) may develop fibrofolliculomas, pneumothorax and/or renal cell carcinoma (RCC). Currently, all patients with pathogenic FLCN variants are recommended to have renal surveillance. It has however been suggested that some FLCN variants only cause pneumothorax, which would make surveillance unnecessary in certain cases. This review assesses this possibility. We provide an up-to-date analysis of clinical and genetic features of BHDS. The PUBMED database was systematically searched to find all articles describing patients with pathogenic FLCN variants. The relevant clinical and genetic features of these patients were recorded and analysed. The prevalence of pneumothorax, pulmonary cysts, RCC and characteristic skin lesions in BHDS were 50.9% (n = 1038), 91.9% (n = 720), 22.5% (n = 929) and 47.9% (n = 989), respectively. There was a higher prevalence of pneumothoraces (p < 0.0001) but lower prevalence of dermatological findings (p < 0.0001) in patients from East Asia compared to North America or Europe. Of the 194 pathogenic FLCN variants, 76 could be defined as 'pneumothorax-only'. Pneumothorax only pathogenic variants (POPVs) were distributed throughout the gene, and there were no statistical differences in variant type. The majority of POPVs (65/76) affected no more than three individuals. Individuals with 'POPVs' also tended to be younger (45 vs. 47 years, p < 0.05). Many apparent POPVs in the literature could result from variable expressivity, age-related penetrance and other confounding factors. We therefore recommend that all individuals found to carry a pathogenic FLCN variant be enroled in lifelong surveillance for RCC.

Fig. 1. Study selection PRISMA diagram.

Articles published between 1st July 1974 and 1st March 2021 were identified in PUBMED and screened as identified.

Fig. 2. Pathogenic FLCN variants.

A Missense/in-frame variants in red, frameshifts in blue, nonsense variants in light green, large deletions/duplications in orange. Bars are proportional to numbers of affected individuals, for mutational hotspots the number of individuals is given above each bar. ‘Pneumothorax-only’ pathogenic variants (POPV) shown above exons, all other variants shown below. B Histogram of individuals affected by POPV (red), all other variants (purple). C Ages of individuals reported to carry POPV (red) or all other FLCN variants (purple) (colour figure online).